I'm pretty sure you can take the GED before you're 18. You can likely enroll at a community college if you've done that. It's what I considered doing when I was 16, and now, a good long while later, wish I had. All the last couple years did was make me more discouraged and lazy. First ~3 semesters at No-Name State University were just a repeat of material from 7th(!) to about December of 12th grade, could have been working on that for college credit much earlier. Pointless. Could have had a better "story" to sell myself to a a nicer school, more time working the tech job I already had in high school and making money, and a bunch of college credit (transferable or not, at least I'd have it) to my name by age 18.

Bonus: once I went to college I found that 15hrs of 100-200 level college courses took up one hell of a lot less of my time than high school plus the ~2.5-3hrs of homework they assigned a night (I understand that part's even worse these days—what a joke). Like, under half as much. Waste of a couple good years. I'd strongly recommend giving that plan consideration, to anyone who thinks they can pass the GED and is having anything other than an outstanding time in high school.